I've noticed that sometimes, people have a hard time noticing stunting. I found it very hard to notice at first, but now it's pretty easy.
I always look at the size of the eyes compared to the head first - this is the easiest way to spot stunting. I'll use my own fish, Watermelon, as an example. She's been in a 13 gallon for about 3/4 year with terrible maintenance (I was a bad owner back then ) and that caused stunting. Causes of stunting are bad water parameters or a certain hormone that prevents growing when there's too much in the water. This is why water changes are important
This is a picture of her in the 13 gallon.
As you can see, her eyes are BIG compared to her head. This is because when stunting, organs, eyes and fins continue to grow, when the body doesn't. This way, stunting can damage internal organs and cause diseases - for example, when the reins break, it can cause dropsy.
This is a picture of how Watermelon looks now:
As you can see, she has grown a lot, and her eyes aren't as big as they were back then. She looks a lot better compared how she looked back then. So it doesn't mean that your stunted fish can't live a happy life
Another indication of stunting is long fins, but this doesn't affect all fish. I've noticed that short-tailed species don't get very large fins, but they are still stunted.
So, if your fish is already stunted, you can't really help it, just be a good mommy or daddy But when buying a new fish, I recommend picking the fish with the smallest eyes.
I hope this helps some people ^_^
PS: did I post this in the right section by the way? I'm not sure..